1. Field of Invention
This invention relates generally to automobiles whose wheels have mounted thereon extended mobility tires, making it possible for the vehicle to run with a flat tire, and more particularly to a vehicle of this type whose tired front wheels have a width and a diameter which differ from those of the tired rear wheels whereby the automobile runs more efficiently than an automobile having four like tired wheels.
2. Status of Prior Art
Automobile is a generic term which encompasses various types of vehicles having a pair of front wheels and a pair of rear wheels, such as passenger cars, station wagons, taxis and vans. The wheels of an automobile are provided with pneumatic tires; hence when a conventional tire is punctured it loses air and goes flat, at which point the flat tire starts flapping on its rim. Since a car having a flat tire cannot continue to run, the flat tire must be replaced with an inflated tire in order to resume operation.
It is for this reason that every automobile now carries in its trunk or elsewhere in the vehicle a spare tire. The replacement of a flat tire at the side of a heavily-travelled road can be a dangerous experience, particularly at night, for one has to jack up the car under difficult conditions, detach the wheel having the flat tire from its axle, and then mount the spare tire thereon.
The need for a spare tire to replace a flat tire dictates that all four tired wheels in the car be identical, otherwise one could not replace whichever one of the front and rear wheels went flat. And since all four wheels of the automobile must be identical, this precludes an automobile tire configuration having wheels which differ in diameter and width.
Thus if one were to construct a motor vehicle of the type shown in the Eisenhuth patent 660,396, having front wheel tires whose diameter is smaller than the diameter of the rear wheel tires, or construct a vehicle of the type shown in the Turner U.S. Pat No. 2,046,042 in which the front wheel tires have a greater diameter than the rear wheel tires, these vehicles could not be provided with a single spare tire. It would be necessary instead to provide a first spare matching the front wheel tires, and a second spare matching the rear wheel tires.
A recent innovation in tire design is of practical significance, for it does away entirely with the need to provide an automobile with a spare tire. This innovative tire, known as an extended mobility tire, is now commercially available as Goodyear's Eagle FV-GS tire and as Michelin's MXV4ZP (Zero-Pressure) tire.
An extended mobility tire, more popularly known as a run-flat tire, has thicker and stiffer sidewalls than a conventional pneumatic tire, and is able therefore to support the weight of the car and its driving dynamics even without air pressure. These run-flat tires are designed to run up to 200 miles at 55 mph with zero air pressure. Thus should a run-flat tire on a vehicle go flat, the vehicle can continue to be driven until a repair station is found that can repair and reinflate the tire.
Extended mobility tires not only dispense with the need for a spare tire, but also with the need for a hydraulic or mechanical jack and other tools stored in the trunk of the automobile which a spare tire make necessary. As a consequence, more room is now available in the trunk. And these run-flat tires relieve the owner of an automobile of the burden of changing flat tire.
But an unexpected advantage of extended mobility tires is that since it does away with the need for a spare tire it also cancels the requirement that the front wheels of the car match its rear wheels.
The introduction of run-flat tires now makes it possible to so configure the front and rear wheels of a car so that they more efficiently perform their assigned functions. Thus when the wheels in the car are steerable, its design must take into account the difficulties which are encountered when changing wheel direction. And when wheels are to be braked, one must consider the ability of these wheels to frictionally engage the road surface and thereby arrest movement of the vehicle.